This paper presents the results of experimental tests of a new proof mass actuator that can be used to implement a velocity feedback loop to reduce the flexural vibration of large flexible structures. Classical proof mass actuators used in vibration control systems require low fundamental resonance frequency to produce a constant force effect at the control position in the desired frequency range. The actuator considered in this study uses a piezoelectric stack transducer, which is characterised by large force and small stroke properties. Thus, to meet the requirement of low resonance frequency, the actuator should be equipped with a large proof mass. However, in this case when the actuator is exposed to shocks the piezoelectric transducer undergoes large deformations, which may lead to cracks. Also, the bulky proof mass limits the range of applications in which the actuator can be used. The actuator presented in this paper includes an additional flywheel element that produces an apparent mass effect without increasing the proof mass. As a result, the fundamental resonance frequency of the actuator is lowered without increasing the total weight of the suspended mass. This leads to both a more robust feedback loop with higher vibration control performance and a more robust actuator to shocks and large disturbances. The paper presents the measured frequency responses functions that characterise the electro-mechanical response of the proposed flywheel piezoelectric actuator, which are contrasted with simulations obtained from a simplified lumped parameter model.
This paper discusses the design and testing of a new velocity sensor, designed to be used in combination with a piezoelectric patch actuator to form a closely located sensor-actuator pair for the implementation of active damping. The velocity sensor consists of a principal spring-mass seismic sensor with an embedded direct velocity feedback control loop. This internal feedback loop uses a control spring-mass seismic sensor and a reactive actuator which are fixed on the seismic mass of the principal sensor. The control gain is tuned to obtain two effects: first the output signal from the principal sensor becomes directly proportional to the base of the sensor itself and second, the fundamental resonance of the principal seismic sensor is cut down by the active damping effect of the internal loop. The background concepts of this sensor are first reviewed. The practical feasibility is then studied considering a prototype model. The stability of the internal feedback control loop has been assessed first. Following this, the frequency response function of the sensor without and with the internal feedback loop has been measured. The experimental measurements have shown that the internal feedback loop is conditionally stable but guarantees enough gain margins in order get the necessary control action to obtain the desired velocity output from the sensor. The sensor has been successfully tested with a closed loop, and shows the desired velocity output with no resonance at the fundamental natural frequency of the seismic sensor.
Using self-sensing in an electrodynamic actuator for broadband active vibration damping requires compensation of the actuator resistance and of the self-inductance of the actuator with an appropriate shunted circuit. In order to reduce power consumption the actuator resistance should be small, but for robustness of self-sensing and a large bandwidth a large resistance is required. A high transducer coefficient is important to get high sensitivity of the induced voltage that is proportional to the vibration velocity of an attached mechanical structure. However, a large transducer coefficient implies a strong magnetic field that also increases the self-inductance so that the measurement bandwidth potentially is reduced. In this study, in order to eliminate the first trade-off between power consumption and robustness, an actuator with a primary driving coil and a secondary measurement coil is proposed. The primary coil is optimized for driving by choosing a small resistance, whereas the secondary coil is optimized for sensing by choosing a large resistance. It has been shown that the transformer coupling between the two coils could be reduced by decreasing the cross section of the secondary coil, but there is a geometric limit on the reduction of the cross section of the secondary coil. Therefore an analogue electronic compensation scheme is proposed to compensate for the transformer coupling between the primary and the secondary coil. Feedback of the sensed velocity in the secondary coil is implemented and experimental vibration damping results at a plate are presented. Results are compared to self-sensing vibration damping, active vibration damping using a velocity sensor and passive damping means of the same weight as the actuator.
Shunt damping for piezoelectric actuators has been extensively studied using passive, tuned or negative capacitance components. Recently it has been noted that a capacitor together with a negative resistance amplifier can also be used for shunt damping using electrodynamic actuators with a low cut-off frequency. However simulations presented in this study indicate that this method is not appropriate for electrodynamic actuators with a high electrical cut-off frequency. This study compares experimental and simulation results of three control approaches obtained with a simple electrodynamic shaker that has a high electrical cut-off frequency: first, proportional current feedback; second, induced voltage feedback estimated with a Wheatstone bridge and third, induced voltage feedback estimated with an Owens bridge which compensates for the inductance of the shaker. The study shows that induced voltage feedback using an Owens bridge results in a negative inductance component that is an appropriate means to obtain vibration damping of a single degree of freedom system. Imperfect tuning to the magnetic parameters and interaction with power amplifier dynamics limit the bandwidth.
This paper summarizes the experimental work carried out to develop a prototype smart panel with sixteen decentralized vibration control units for the reduction of sound radiation. The system studied consists of a thin aluminum panel of dimensions lx × ly = 414 × 314 mm and thickness 1 mm with an embedded array of 4 × 4 square piezoceramic actuators. The sensing system equally consists of an array of 4 × 4 accelerometers that are arranged in such a way as to match the centre positions of the sixteen piezoceramic patches. Each of the sixteen sensor actuator pairs is set to implement decentralized velocity feedback control.
In this paper the design of the sixteen modular sensor-controller-actuator systems is discussed in detail. The open loop sensor- actuator measured frequency response function is first analysed and contrasted with that derived from simulations, in a frequency range up to 50 kHz. This analysis is mainly focussed on the higher frequency effects due to the size of the piezoelectric actuator and generated by the dynamics of the accelerometer sensor. The stability of one or all sixteen control units are assessed experimentally using the Nyquist criterion. The reduction of sound radiation and panel vibration is then assessed with reference to a primary force excitation acting on the panel.
This paper presents a study of a distributed arrangement of double PVDF actuator/sensor pairs bonded on a cantilever beam for the control of vibration at the tip. The arrangement of a single PVDF actuator/sensor pair, in practice, is known to be non-minimum phase due to coupling between in-plane motion and out-of-plane motion. This means that a single pair arrangement does not have the conventional driving-point collocated system property. The stability and performance of the arrangement are limited by finite feedback gains, which can be used with direct velocity feedback control. A double pair arrangement using four layers of PVDF has thus been suggested to overcome this problem. Theoretically, when both the actuator pair and the sensor pair are working out-of-phase, then the response becomes minimum phase since in-plane motion cannot be excited or detected. A smart beam with double PVDF actuator/sensor pairs has been implemented. A triangular shaped actuator/sensor pair was bonded on each side of the beam. The initial experimental measurements with individual pairs of transducers showed a good reciprocity and a strong coupling between out-of-plane and in-plane responses. All the four layers have then been used as out-of-phase actuators and sensors to attempt to measure only the out-of-plane response. However, in practice, this compensation method was found not to discriminate against the in-plane response, due to the direct coupling between the actuation and sensing transducers due to their finite thickness and compliance. Therefore, the four layers smart beam does not have a minimum phase property. A new arrangement of actuator/sensor pair for in-plane compensation is then suggested and discussed.
The active control of a structure in order to reduce its vibration or sound radiation, which may be termed active vibro-acoustic control, has previously been achieved with multiple actuators and sensors and fully-coupled feedforward or feedback controllers. In this paper local velocity feedback using multiple miniature accelerometers will be investigated, together with either collocated force actuators or piezoceramic actuators placed under each sensor. With ideal force actuators, the plant response is passive for such an arrangement of collocated actuator/sensor pairs and so decentralized (local) feedback is guaranteed stable. This property is shown to extend to collocated velocity sensors and piezoceramic actuators over the bandwidth of interest and so multiple local feedback loops are also predicted to be stable. The performance of such a system is simulated in controlling the vibration and sound transmission through a thin plate, excited by an acoustic plane wave, with a 4 x 4 array of such actuator/sensor pairs, which are connected together with 16 local feedback control loops. Using force actuators, significant frequency-averaged reductions up to 1kHz in both the kinetic energy (28dB) and transmitted sound power (18dB) can be obtained with an appropriate feedback gain in each loop. These reductions are not so great with piezoelectric actuators (12dB and 9dB respectively) but their use allows the controller to be fully integrated in the structure.
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